This invention relates to an ultrasonically-driven rotary device and, more particularly, a rotary dental polisher device.
One of the most widely accepted new dental instruments of recent years is the ultrasonic dental prophylaxis device. Such devices have a power unit which converts AC line-frequency electrical power into higher frequencies and a flexible cable which carries the higher frequency power to a hand held, tubular housing. An insert for the device has a sleeve for releasably connecting the insert to the housing and for supporting a vibrator. One end of the vibrator projects into the housing and is a magnetostrictive or other transducer device responsive to the higher frequency electrical excitation means in the housing for producing longitudinal ultrasonic vibrations in the vibrator. The other end of the vibrator is the dental tool. The two ends of the vibrator are usually connected by a connecting body which, by a reduction in diameter or change in acoustic impedance, amplifies the ultrasonic vibrations at the tool. The whole vibrator is also an integral multiple of one-half the wavelength of the ultrasonic vibrations in the vibrator to be resonant for maximum vibration and to have at least one node of ultrasonic vibration. The sleeve is usually arranged to support the vibrator at the node to avoid damping the vibrations.
The tool end of the vibrator has at least one bend which converts the longitudinal ultrasonic vibrations in the vibrator into ultrasonic elliptical motion at the tool end as described in the assignee's U.S. Pat. No. 2,990,616. The elliptical motion of the tool is there used to dislodge ultrasonically calculus, plaque and other matter adhered to teeth, particularly along the gum line. Removing calculus and plaque from teeth by hand is well known for the periodontal and hygienic treatment of teeth, and the ultrasonic dental prophylaxis unit provides similar treatment with the improvement and assistance of ultrasonic vibrations, in the way of a power tool.
In addition to removing calculus and plaque, however, teeth often require polishing or abrasive brushing to remove stains and otherwise clean broader areas of the teeth more rapidly. Such polishing is generally accomplished with a relatively low-speed rotary rubber cup or brush and a polishing compound. Periodontists and hygienists have thus required two pieces of equipment, the ultrasonic dental prophylaxis device and a rotary polisher.
Rotary polishers have, until now, generally been driven by dental drilling equipment, but another recent innovation in dentistry presents its own, further problem for the relatively low speed rotary polishing of teeth. This innovation is the high speed air turbine dental drill. Its very high rotational speeds on the order of 10.sup.5 rpm are desirable for dental drilling, but greatly in excess of the rotational speeds suitable for the rotary brushing or polishing of teeth. One limitation on the speeds of such rotary polishing, for example, is retaining the polishing compound on the rotating brush. For this, rotational speeds on the order of 10.sup.2 to 10.sup.3 rpm are desired. If the new air turbine drive is thus to be used for rotary polishing, an expensive speed reduction gear must be provided to achieve the much lower rotary polishing speeds.
Alternatively, the old-fashioned, variable-speed, electrical belt-driven dental drilling apparatus may be used, but such devices with their large, multi-arm belt structures are particulary intimidating to many patients. In addition, three pieces of equipment and two power supplies are then required for a full dental operatory: the electric ultrasonic prophylaxis unit for removing tartar, the high speed turbine drill and air power supply for drilling of teeth, and the electric belt-driven unit for polishing.
There has thus been for some years a desire to consolidate the various functions both for economic and aspectual advantage. This desire, however, has so far led only to suggestions of combining the rotary drilling and polishing functions with the disadvantages just described, or to combining the ultrasonic prophylaxis and high-speed rotary drilling functions as described in the assignee's U.S. Pat. No. 3,058,218.
This patent discloses a way of rotating a drill at high speeds with longitudinal ultrasonic vibrations. The longitudinal ultrasonic vibrations are produced at a transducer end of a resonant vibrator in an insert connected to a housing and converted into elliptical motion at the other end of the vibrator in the same way as described for the ultrasonic prophylaxis device. The elliptically-moving end of the vibrator under pressure tangentially engages a shaft which is rotatably mounted in or adjacent the vibrator during one arc of the ellipse. The high frequency of the ultrasonic vibrations, generally in a range of from 15 to 50 kHz, however, rotates the shaft at correspondingly high speeds of from 45,000 to 360,000 rpm in the examples in the patent. Such speeds are greatly in excess of those suitable for rotary polishing at least because the polishing compound cannot be retained on the polisher. Thus, even though the patent initially suggests using the ultrasonically driven rotary device for "abrading and polishing operations" such operations must be considered grinding-type polishing and not the brushing-type polishing for cleaning teeth considered here. This is further confirmed by the patent's consistent emphasis of high rotational speeds, as opposed to the low speeds desired for polishing.
The patent also discloses only rotating the drill shaft directly from the elliptically moving end of the vibrator. As the elliptical motions under pressure tangentially engage the shaft during one arc of the ellipse to rotate the shaft unidirectionally, they impart also high-frequency impacts to the shaft. In addition to that, the rotating polisher-tool shaft or drill has some axial thrust applied to it. It has been found difficult, at least economically, to provide a bearing for a directly rotated element or elements as disclosed in the patent which will withstand for longer periods of time these radial and axial forces in the environment of ultrasonic vibrations.